1. Field of the Invention
This invention relates to novel activated Ziegler catalyst compounds employed with co-catalyst for the polymerization of ethylene under essentially homopolymerization conditions, especially to produce linear high density polyethylenes. More particularly, this invention relates to activated Group IVb, Vb, VIb, or VIII transition metal-based catalyst components comprising a solid reaction product obtained by treating a solid, particulate inert support material, in stages, with at least (i) an organometallic composed of a Group IIa, IIb or IIIa metal, (ii) an oxygen containing compound selected from ketones, aldehydes, siloxanes, alcohols or mixtures thereof, (iii) optionally an acyl halide, and (iv) a transition metal compound.
2. Background Art
As is well known, high density polyethylene is a linear polymer with a density.gtoreq.0.94 g/cc and a melting point of about 136.degree. C., made by coordination with Ziegler or Phillips type catalysts, discussed below. Many intermediate density polyethylenes ranging down to about 0.94 density are prepared for various applications by modification of the conditions used for manufacture of the higher density product. For example, controlled amounts of branching of the polymer chain are generated by introduction of terminal olefin (1-olefin) comonomers such as 1-butene or 1-hexene.
Essentially there are two general families of ethylene polymerization catalysts. Generally speaking the Ziegler catalysts historically are prepared by reaction of an aluminum alkyl compound with TiCl.sub.4 or TiCl.sub.3 to give compositions sometimes soluble in hydrocarbon solvents. The Phillips catalysts are insoluble materials historically prepared by deposition of chromium oxides on silica. This invention relates to Ziegler type catalysts and not to Phillips type catalysts.
Colloidal Ziegler catalysts conventionally are prepared by reaction of TiCl.sub.4 with trialkylaluminum compounds in cyclohexane or heptane, which alkylates the titanium compound and reduces it to the trivalent state in the form of a brown floc. Insoluble Ziegler catalysts conventionally are prepared from crystalline TiCl.sub.3. In commercial solution- or slurry-polymerization practice, the catalyst solution or slurry is fed along with ethylene and a hydrocarbon diluent into reactor vessels. In solution processes, the hydrocarbon diluent used, suitably cyclohexane, is a solvent for the polyethylene; in slurry processes, the diluent used, suitably hexane or a light naphtha, is a poor solvent for the polyethylene. In solution polymerization, polymer content of the solution is limited by the viscosity that can be handled, which as a practical matter limits the molecular weight that can be allowed. In the more widely practiced slurry polymerization, the polymer is obtained as a powder, and a high molecular weight material is easily produced. Hydrogen is often used to control the degree of polymerization. Typical operating conditions employ relatively low pressures (10-30 atm.) and temperatures (80.degree. C. to 200.degree. C.). These processes need large reactors and expensive equipment for solvent recovery and drying. The need for solvent recovery and drying equipment is eliminated by gas phase ethylene polymerization, in which no hydrocarbon diluent is required. Instead, ethylene and catalyst in the form of dry powder are fed continuously to a fluidized bed reactor where polymerization takes place at reaction pressures of typically about 20 atm. and at temperatures typically in the range of 85.degree. C.-100.degree. C. A problem with gas phase ethylene polymerization is accurate temperature control of the highly exothermic polymerization reaction in the absence of any hydrocarbon diluent, and associated reactor fouling. A vital requisite to all these processes employing Ziegler type catalysts is high catalytic activities giving yields which avoid the costly process of removing the solid catalyst from the polymer after the reaction, called de-ashing.
Recently, solid catalyst components for use in Ziegler type polymerization with alkyl aluminum co-catalysts have been developed that have (i) high catalytic activities, for efficient yields and good productivity which eliminate de-ashing, (ii) good comonomer incorporation, for producing resins with differing product properties, including density regulation, and (iii) high hydrogen responsiveness, for the control of molecular weight. These catalyst components are described, inter alia, in U.S. Pat. Nos. 4,558,024; 4,558,025; 4,564,606; 4,565,797; 4,634,746; 4,634,747; 4,634,748; 4,634,749; 4,639,428; 4,640,907; and 4,711,865.
In these patents as a group, the catalyst component comprises a solid reaction product obtained by treating an inert solid support material, suitably a particulate, porous material, for example, silica, alumina, magnesia or mixtures thereof, for example silica-alumina, in an inert solvent, in stages, with (A) optionally, Cl.sub.2, Br.sub.2, an interhalogen, or mixtures thereof (U.S. Pat. Nos. 4,564,606; 4,634,747), (B) an organometallic compound of a Group IIa, IIb or IIIa metal wherein all the metal valencies are satisfied with a hydrocarbyl group (all the aforecited patents), (C) an oxygen-containing compound selected from alcohols, aldehydes, ketones, siloxanes, or mixtures thereof (all the aforecited patents), (D) optionally, an acyl halide (U.S. Pat. Nos. 4,558,024; 4,564,606; 4,634,747; 4,711,865; 4,558,025; 4,634,749; 4,640,907; 4,639,428), (E) optionally one or more halogen containing compounds selected from chlorosilanes, Cl.sub.2, Br.sub.2, an interhalogen, or mixtures thereof (U.S. Pat. Nos. 4,634,746; 4,565,797), (F) at least one transition metal compound of a Group IVb, Vb, VIb or VIII metal (all the aforecited patents), (G) optionally, Cl.sub.2, Br.sub.2, an interhalogen, or mixtures thereof (U.S. Pat. Nos. 4,564,606; 4,634,747; 4,711,865), (H) optionally, a Group IIIa metal hydrocarbyl dihalide (U.S. Pat. Nos. 4,558,025; 4,634,749; 4,640,907; 4,639,428; 4,634,748), (I) optionally, Cl.sub.2, Br.sub.2, an interhalogen, or mixtures thereof (U.S. Pat. No. 4,639,428), and (J) optionally, an organometallic compound of a Group IIa, IIb or IIIa metal (U.S. Pat. Nos. 4,634,746; 4,634,749; 4,639,428).
In U.S. Pat. No. 4,558,024, optional step (D) but none of optional steps (A), (E), (G), (H), (I) or (J) is involved.
If steps (D) and (G) are employed, as in U.S. Pat. Nos. 4,564,606 and 4,711,865, then steps (E), (H) and (I) are not employed; and if step (J) is employed, step (A) is not employed, as in U.S. Pat. No. 4,711,865, but if step (J) is not employed, step (A) may be employed.
If step (D) but not step (G) is employed, then as in U.S. Pat. Nos. 4,558,025 and 4,534,749, step (H) is employed and steps (A), (E), and (J) are not employed. Optionally, as in U.S. Pat. No. 4,639,428, step (I) may also be employed, or as in U.S. Pat. No. 4,640,907, the product may be contacted with minor amounts of ethylene to prepolymerize the product.
If step (D) is not employed and if step (J) is employed, then steps (A), (I) and (H) are not employed, as in U.S. Pat. Nos. 4,634,746 and 4,634,747; and if step (E) is performed as in U.S. Pat. No. 4,634,746, unless a chlorosilane is employed in step (E), then step (G) is optional, however, if a chlorosilane is employed in step (E), step (G) is employed.
If step (D) and step (J) are not employed, then step (H) is employed and steps (A), (G) and (I) and (E) are not employed, as in U.S. Pat. No. 4,634,748.
In all the above patents, the inert solid support material can be treated alternatively with (i) simultaneously the (B) organometallic compound and the (C) oxygen-containing compound, (ii) the reaction product of the (B) organometallic compound and the (C) oxygen-containing compound, or (iii) the (C) oxygen-containing compound followed next by the (B) organometallic compound.
For shorthand ease of reference, any of the body of catalyst components encompassed by the foregoing group of patents is sometimes hereinafter referred to as the "solid reaction product catalyst component." These patents are incorporated herein by reference for all purposes, including without limitation for the prior art described in such patents and for details of the specific catalyst component preparation, catalyst systems, and polymerization processes described therein.
In the above cited patents, the solid reaction product catalyst component is used with an aluminum alkyl co-catalyst for the copolymerization of ethylene with other 1-olefins such as propylene, 1-butene, 1-pentene, 1-hexene and 1-octene, or with diolefins such as 1,4-pentadiene, 1,5-hexadiene, butadiene, 2-methyl- 1,3 butadiene, and the like. As mentioned above, terminally unsaturated 1-olefins conventionally are used to prepare reduced density linear polyethylene resins.
For many of these recently developed solid reaction product catalyst components, however, catalytic activity is much lower in the absence of the density lowering 1-olefins such as 1-butene and 1-hexene, and consequently polymerization yields of high density linear polyethylene resins are smaller than copolymerization yields of reduced density linear polyethylene resins.
Although not involving the Ziegler catalyst family of this invention, it may be mentioned that Phillips catalysts have been employed, as disclosed in U.S. Pat. Nos. 4,252,927 and 4,252,928, to polymerize ethylene using diolefins with either trihydrocarbylboron or trihydrocarbyl aluminum.
There yet exists a need for solid reaction product catalysts which are both highly active for the production of high density linear polyethylene resin and which do not significantly lower the density of the polyethylene product.